Progress in the CFD Modeling of Flow Instabilities in Anatomical Total Cavopulmonary Connections CHANG WANG, 1 KEREM PEKKAN, 1,2 DIANE DE ZE ´ LICOURT, 1 MARC HORNER, 3 AJAY PARIHAR, 4 ASHISH KULKARNI, 4 and AJIT P. YOGANATHAN 1 1 Wallace H. Coulter School of Biomedical Engineering, Georgia Institute of Technology, Room 2119 U. A. Whitaker Building, 313 Ferst Dr, Atlanta, GA 30332-0535, USA; 2 Department of Biomedical Engineering, Carnegie Mellon University, Pittsburgh, PA, USA; 3 ANSYS Inc., Evanston, IL, USA; and 4 Fluent India Pvt Ltd, Pune, India (Received 21 May 2006; accepted 6 July 2007; published online 20 July 2007) Abstract—Intrinsic flow instability has recently been reported in the blood flow pathways of the surgically created total-cavopulmonary connection. Besides its contribution to the hydrodynamic power loss and hepatic blood mixing, this flow unsteadiness causes enormous challenges in its compu- tational fluid dynamics (CFD) modeling. This paper inves- tigates the applicability of hybrid unstructured meshing and solver options of a commercially available CFD package (FLUENT, ANSYS Inc., NH) to model such complex flows. Two patient-specific anatomies with radically different tran- sient flow dynamics are studied both numerically and experimentally (via unsteady particle image velocimetry and flow visualization). A new unstructured hybrid mesh layout consisting of an internal core of hexahedral elements surrounded by transition layers of tetrahedral elements is employed to mesh the flow domain. The numerical simula- tions are carried out using the parallelized second-order accurate upwind scheme of FLUENT. The numerical vali- dation is conducted in two stages: first, by comparing the overall flow structures and velocity magnitudes of the numerical and experimental flow fields, and then by com- paring the spectral content at different points in the connection. The numerical approach showed good quantita- tive agreement with experiment, and total simulation time was well within a clinically relevant time-scale of our surgical planning application. It also further establishes the ability to conduct accurate numerical simulations using hybrid unstructured meshes, a format that is attractive if one ever wants to pursue automated flow analysis in a large number of complex (patient-specific) geometries. Keywords—Fontan operation, Digital particle image veloc- imetry (DPIV), Flow instability, Computational Fluid Dynamics (CFD), Patient specific, Surgical planning, Total Cavopulmonary Connection (TCPC). INTRODUCTION The Total Cavopulmonary Connection (TCPC) is the preferred procedure for surgical repair of single ventricle heart disease. This surgical procedure in- volves the anastomosis of the inferior vena cava (IVC) and superior vena cava (SVC) to the pulmonary arteries (PA) such that the right side of the heart is by- passed to prevent the pathological condition due to the mixing of oxygenated and deoxygenated blood inside the heart. 16 The resultant TCPC morphologies, how- ever, introduce non-physiologic complexities for the blood flow. In vitro experimental studies 15,23 as well as previous computations 7,15 have shown that given a steady inflow condition with flow rates within the laminar regime, highly unsteady vortical motion is persistently created within the connection region. The unsteadiness manifests itself in the form of seemingly chaotic meandering of the flow recirculation into PA and venae cavae. The onset of this complex three- dimensional (3D) flow is a consequence of non-linear 3D flow instabilities generating small-scale perturba- tions at the stagnation region where the SVC and IVC flows collide. This highly disturbed flow pattern is characterized by regions with high velocity gradients and is therefore very dissipative. An accurate predic- tion of the detailed transient flow evolution is critical to the evaluation of the energy loss within the con- nection, which is the primary variable for evaluating the efficiency and consequently optimizing the TCPC design. 10 Recent lumped parameter modeling studies 21 have shown that venous power loss has a significant impact on cardiac output and venous blood volume share in single-ventricle circulation. Advances in fluid flow modeling of complex TCPC anatomies is even more critical as new virtual patient-specific surgical planning tools are introduced 28 and proven to be potentially useful in several clinical cases. 22,32 Accurate Address correspondence to Ajit P. Yoganathan, Wallace H. Coulter School of Biomedical Engineering, Georgia Institute of Technology, Room 2119 U. A. Whitaker Building, 313 Ferst Dr, Atlanta, GA 30332-0535, USA. Electronic mail: ajit.yoganathan@ bme.gatech.edu Annals of Biomedical Engineering, Vol. 35, No. 11, November 2007 (Ó 2007) pp. 1840–1856 DOI: 10.1007/s10439-007-9356-0 0090-6964/07/1100-1840/0 Ó 2007 Biomedical Engineering Society 1840